1. Technical Field
The present invention relates to an electrophotographic photosensitive body and a photoconductive paint, and specifically it relates to an electrophotographic photosensitive body with excellent imaging properties, electrical characteristics and stability against environmental changes, and which provides superior printing resistance, desensitization reactivity and desensitized coating formability when used for electrophotographic lithographic printing plates, as well as to a photoconductive paint of which the electrophotographic photosensitive body is composed.
2. Description of the Related Art
Electrophotographic photosensitive bodies composed of conductive substrates and photoconductive layers are employed in the common electrophotographic process known as the Carlson process, i.e. for formation of images by electrification, exposure and development, and they are also employed in a broad range of practical methods as plates for lithographic printing after image formation.
Binding resins used for formation of photoconductive layers of electrophotographic photosensitive bodies are required to have satisfactory film-forming properties, adhesion to photoconductive layers formed on conductive substrates, and dispersion of inorganic photoconductive powders in the binding resins, as well as suitable performance in terms of imaging properties and electrical characteristics for electrophotographic photosensitive bodies, and must also maintain stable performance regardless of changes in the environment during imaging.
When used for photoconductive paints, consistently stable dispersion of inorganic photoconductive powders is a requirement.
Silicone resins, alkyd resins, acrylic resins (acrylic ester copolymers, etc.) and mixtures of such resins have long been publicly known as resins used for electrophotographic photosensitive bodies and photoconductive paints.
However, the use of these conventional resins has been associated with a number of problems, including:
1) a lack of affinity with inorganic photoconductive powders, and poor dispersion when prepared as photoconductive paints;
2) Inferior reproducibility of photographed images;
3) Susceptibility to environmental changes during imaging (temperature and humidity fluctuations);
4) When used for lithographic printing plates, insufficient film strength and adhesion of photosensitive layers, resulting in inconveniences such as peeling of photosensitive layers during printing;
5) With lithographic printing plates, low reactivity with desensitizing fluids and generation of scum during printing.
As an improvement for photoconductive layer binding resins there has been disclosed a process which provides enhanced imaging properties, electrical characteristics and humidity resistance, using an acrylic resin with an acid value of 4-50, in a combination of a component with a molecular weight distribution of 10.sup.3 -10.sup.4 and a component with a molecular weight distribution of 10.sup.4 -2.times.10.sup.5 (Japanese Unexamined Patent Publication No. 60-10254).
Research is diligently being pursued on lithographic printing plates employing electrophotographic photosensitive bodies, and there has been disclosed a binding resin for photoconductive layers which exhibits both the imaging properties and electrical characteristics of electrophotographic photosensitive bodies and the printing properties of printing plates, wherein, for example, a resin with a molecular weight of 1.8.times.10.sup.4 -10.sup.5 and a glass transition point of 10-80.degree. C., obtained by copolymerizing a (meth)acrylate monomer with another monomer in the presence of fumaric acid, is combined with a copolymer comprising a (meth)acrylate monomer and another monomer other than fumaric acid (Japanese Unexamined Patent Publication No. 50-31011).
Also disclosed is the use of quadripolymers or pentapolymers containing acrylic acid and hydroxy (meth)acrylate (see Japanese Unexamined Patent Publication Nos. 54-20735 and 57-202544), and the use of terpolymers containing (meth)acrylic acid esters substituted with alkyl groups of 6 or more carbon atoms and carboxylic acid-containing vinyl monomers has been described as having an effect of improving desensitizing properties of photoconductive layers (Japanese Unexamined Patent Publication No. 58-68046).
Nevertheless, actual evaluation of resins considered to have the aforementioned effects in terms of imaging properties, electrical characteristics and humidity resistance reveals that even they are not satisfactory in practice, in terms of their antistatic properties, electrical characteristics such as retention of light damping and darkness damping, and imaging properties such as degree of scum on non-image sections and image density, or in terms of their stability against environmental changes during imaging; an additional problem has been their weak coating strength on photoconductive layer surfaces, which leads to abrasion damage to surfaces and indentation smudges on imaged objects and printed products.
Even in the case of binding resins considered to have effects of improving desensitizing properties of lithographic printing plates, actual evaluation shows that when desensitizing treatment is carried out by hand etching, which gives a high desensitizing treatment effect, some slight degree of spotted scum is produced, but when desensitizing treatment is carried out using etching processors which have become popular in recent years and have a low desensitizing treatment effect, scum is produced over the entire surface.
Thus, when desensitizing treatment is carried out using an etching processor, it is common to employ a method whereby treatment is effected twice with the processor. However, although such repeated treatment methods have an effect on scum produced over the entire surface, there is a high tendency toward spotted contamination on the printed product, compared to hand etching treatment which has an effect against spotted scum.